How might US history have been different if, during Reconstruction, the plantations of the South had been divided, and ex-slaves had been given plots of land and the means to farm them?

Answer:

Instead of the Northern banks and outlaws seeking to take what they could, the South would have prospered again under a new sense of independence. The US economy by the turn of the century would have been 2nd to none! In other words, what would have happened if the "Forty acres and a mule" vow had been kept? A significant number of former slaves would have been killed, terrorized to leave, or forced to become "sharecroppers" of white-owned working land because no white man would purchase their produce. The end of the Civil War did not put an end to racial hatred just witness today's media conglomerates' vile conduct against such on-air bigots as Don Imus - the slime is back on the air! Black folks would have learned that nothing but more suffering would have given them those forty acres. There were hundreds of hate groups which, exemplified by the KKK, continued to make life difficult for them. And we would have ended up just where we are today in the USA in terms of race relations and human rights: a land wallowing in its own hypocrisy. A promise many formerly enslaved people claimed the U.S. government had made at the end of the Civil War was represented in the expression "Forty Acres and a Mule". A rumor circulated across the South that formerly enslaved people would be given land belonging to enslavers so that they could set up their own farms.

Reference

Roy, F., & Hahn, S. (2006). The Roots of Southern Populism: Yeoman Farmers and the Transformation of the Georgia Upcountry, 1850-1890. Oxford University Press.

Saville, J. (1996). The Work of Reconstruction: From Slave to Wage Laborer in South Carolina 1860-1870. Cambridge University Press.